It was Kelly's (sp?) job to keep track of WH staff. If people are screwing up, they can be counseled, asked to change and ultimately fired if they are causing harm to the country or the administration. I do believe Trump had no idea Kelly gave her the boot. On KPCC the other day a media professor indicated there were numerous reports of Amorosa taking advantage of perks, staff, etc.,.and acting strangely.
Once fired she began her tape campaign and statements re Trump which may or may not be true.
All Trump had to do was rise above it, stay out of it and let her self destruct. Act like the President of the United States. A few lines of sympathy maybe, "I understand why Ms. Amorosa is upset; she was in an important position. I wish her well in her new endeavors." Leave it at that. But no, he's got to act like a bozo, give her credibility, respond in kind, call her a dog. This is the POTUS for goodness sake-act like it.
But, he can't because he is so insecure, afraid people will think he's weak. His backers will say, "He's tough, he's fighting back." It shows how small they are. They believe a president should be involved in a twitter war with a woman who would have soon lost her grip.
Trump has lowered the prestige of the office, lowered our standing throughout the world.